In the implementation of an optical device, it is frequently necessary to switch an optical component between defined positions. In such cases, it is desirable for the optical component to be firmly held in the defined positions, but to be freely moveable therebetween without the exertion of undue force.
Although not so limited, the present invention finds particular applicability to a night vision device having an infrared light emitting diode (LED) for providing illumination. The LED is located in an LED port in a housing, and it is desirable to be able to use it either as a spot light or as a flood light.
For use as a spot light, a lens assembly is provided, which is moved over the LED port to a defined position to accomplish focussing of the light from the LED. On the other hand, for use as a flood light, the lens assembly is moved to another defined position where it does not interact with the light from the LED, allowing the light to spread to its full extent.
In a known prior art design, the lens assembly could “stick” in either position, and it would take a great deal of force to move it towards the other position, so that it could slam into the other side. The design employed two small protrusions (nubs) in the upper wall of a large slot in the front of the binocular housing. The large slot served as a track for the lens assembly to travel in. Specifically, the lens assembly has a cylindrical member projecting from a flange with two flats that slide snugly in the large slot. Centered within the flats of the flange there is a small cylindrical groove. This small cylindrical groove provides an area for the nubs to engage with, creating a detent. The flange is captured in the large slot of the binocular housing by way of a retainer plate. The close spacing and tight tolerances of the design were part of the reason why the nubs held-on to the small grooves. The geometry of the grooves also lent themselves to difficult release, making for an abrupt transition from detented-to-free-to-detented again positions.